(a) Field of the Invention
The present invention relates to an OFDM (orthogonal frequency division multiplexing) wireless communication system operable on a frequency-selective channel. More specifically, the present invention relates to a channel compensation system and method thereof.
(b) Description of the Related Art
Recently, OFDM methods, which are digital modulation methods for improving data rates per communication bandwidth and preventing interference caused by a multipath fading channel, have been widely used for communication methods for providing mobile multimedia services.
For example, the OFDM methods are adopted for cable communication methods of the ADSL and VDSL systems, used for radio standards of digital audio broadcasting and digital video terrestrial broadcasting, and in addition, they are standardized as IEEE802.11a and 802.16 for W-LAN communication methods of from 2.4 to 5 GHz.
When transmitting high-rate data through a mobile channel in the above-noted OFDM system, the mobile channel is modeled as a frequency selective fading channel, and this kind of the OFDM wireless communication system adds a guard interval obtained from a cyclic extension to an OFDM signal and transmits them so as to solve inter-symbol interference caused by a delay spread of the frequency selective fading channel.
In detail, the conventional OFDM wireless communication system provides an IDFT (inverse discrete Fourier transform) unit and a DFT (discrete Fourier transform) for data modulation and demodulation to a transmitter and a receiver. When the receiver receives a signal from the transmitter, and demodulates the signal by using the DFT unit, the demodulated frequency selective fading channel signal is represented in a product format of a transmit signal. Through this, a channel predictor of the receiver predicts an amplitude and a phase of the channel represented in the product format by using a pilot symbol, and performs channel compensation by using the predicted amplitude and the phase of the channel. That is, the channel compensation is performed by multiplying the demodulated OFDM signal by a complex conjugate that is a channel predict value, which executes channel compensation more simply and easily than the conventional channel compensation following a convolutional operation.
However, the conventional channel compensation method is of no consideration in a case when the amplitude of the channel steeply reduces, and lowers the total performance caused by generation of burst errors. Further, the channel compensation method increases BER (bit error rates) and allows low data rates.
A single carrier communication system uses results of the channel predictor to perform channel compensation so as to compensate the frequency selective fading channel, but this channel compensation method has a demerit of using a channel predictor and a complex equalizer.
Therefore, a channel compensation system and method for reducing the BER of an interval with a narrow channel amplitude in the OFDM wireless communication system is required.